Electrosurgical generator and system

ABSTRACT

An electrosurgical system includes a generator for generating radio frequency power, and an electrosurgical instrument including at least three electrodes and. The generator includes a radio frequency output stage having at least a pair of RF output lines, and a power supply coupled to the output stage for supplying power to the output stage. A controller is operable to limit the radio frequency output voltage developed across the output lines to at least a first predetermined threshold value to produce a cutting RF waveform, and a second threshold value to produce a coagulating RF waveform. In a combined mode, the controller delivers both cutting and coagulating waveforms, either simultaneously or by alternating constantly between the first and second threshold values to form a blended signal. The system also includes means for feeding the waveform to the three or more electrodes such that the cutting RF waveform is delivered between a first pair of the electrodes, and the coagulating waveform is delivered between a second pair of the electrodes.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part of U.S. application Ser. No. 11/260,189filed Oct. 28, 2005, which is a divisional of U.S. application Ser. No.10/378,676 filed Mar. 5, 2003, now U.S. Pat. No. 6,966,907, issued Nov.22, 2005, which is a continuation-in-part of U.S. application Ser. No.10/228,284 filed Aug. 27, 2002, now U.S. Pat. No. 6,984,231, issued Jan.10, 2006, which claims the benefit of Provisional Application No.60/314,650, filed Aug. 27, 2001, the entire contents of suchapplications and patents being incorporated by reference in thisapplication.

FIELD OF THE INVENTION

This invention relates to an electrosurgical generator, and to anelectrosurgical system comprising a generator and an electrosurgicalinstrument with two or more treatment electrodes. Such systems arecommonly used for the cutting and/or coagulation of tissue in surgicalintervention, most commonly in “keyhole” or minimally invasive surgery,but also in laparoscopic or “open” surgery.

BACKGROUND OF THE INVENTION

It is known to provide electrosurgical generators which providedifferent radio frequency signals for cutting and coagulation, and alsoto provide a blended signal in which the generator rapidly alternatesbetween the signals for cutting and coagulation. Our U.S. Pat. No.6,416,509 and also U.S. Pat. No. 3,885,569 to Judson describe blendedsignals of this type.

SUMMARY OF THE INVENTION

The present invention provides an improvement to this type ofelectrosurgical system, in that the cutting and coagulation waveformsare delivered to different electrodes of the electrosurgical instrument.Accordingly, there is provided an electrosurgical system including agenerator system for generating radio frequency (RF) power, and anelectrosurgical instrument including at least three electrodes, thegenerator system comprising one or more sources of RF output power, anda controller operable to control the generator system such that it iscapable of delivering a first cutting RF waveform to the electrosurgicalinstrument or a second coagulating RF waveform to the electrosurgicalinstrument, and, in a combined mode, to deliver both first and second RFwaveforms, the system also including means for feeding the waveform tothe three or more electrodes such that, in the combined mode, thecutting RF waveforms is delivered between a first pair of the three ormore electrodes, and the coagulating RF waveform is delivered between asecond pair of the electrodes.

Our pending European patent application EP 02255826.6 describes anelectrosurgical system in which the operator can select between acutting signal and a coagulation signal. When the cutting signal isselected, it is supplied to one pair of electrosurgical electrodes, andwhen the coagulation signal is selected it is supplied to a differentpair of electrosurgical electrodes. The present invention is animprovement to this system, in that it also provides a combined mode ofoperation, but with the different components of the combined signalbeing supplied to different sets of electrosurgical electrodes.

The “combined mode” of the generator can be provided in different ways.In one arrangement, the generator system comprises a single source ofradio frequency power, and, in the combined mode, the controller isoperable to cause the generator system to alternate constantly betweendelivering the first cutting RF waveform and the second coagulating RFwaveform. This is the more traditional “blended” signal of U.S. Pat. No.6,416,509 and U.S. Pat. No. 3,885,569. Alternatively, the generatorsystem comprises at least first and second sources of radio frequencypower, operating at different frequencies, the first source of radiofrequency power being adapted to deliver the first cutting RF waveform,and the second source of radio frequency power being adapted to deliverthe second coagulating RF waveform, and, in the combined mode, thecontroller is operable to cause the generator system to deliver both thefirst and second RF waveforms simultaneously. This is a differentarrangement in which the output of two RF sources is supplied to theinstrument simultaneously. Both arrangements have the effect, however,of supplying both cutting and coagulating RF signals to theelectrosurgical instrument while the instrument is in use.

Where the alternating blended signal is employed, the means forconnecting the waveform conveniently comprises a switching circuit forvarying the connections between the source and the three or moreelectrodes such that, in the combined mode, a first part of the combinedsignal that is the cutting RF waveform is delivered between a first pairof the three or more electrodes, and a second part of the combinedsignal that is the coagulating RF waveform is delivered between a secondpair of the three or more electrodes.

In a convenient arrangement, the switching circuit of the generator issuch that, in the combined mode, the connections between the powersupply and the electrodes are switched such that the first part of theblend signal is delivered between the first and second electrodes, andthe second part of the blend signal is delivered between the second andthird electrodes. In this arrangement, there is a common electrode whichis used in both the cutting and coagulation operations, but it isequally feasible to have completely different pairs of electrodes foreach function.

Preferably, the switching circuit comprises first and second inputconnections, first second and third output connections, and anelectronic switch connected between the first and second outputconnections, and being adapted to open and close in order to connect thefirst and second output connections periodically one to the other. Theelectronic switch conveniently opens and closes at a frequency ofbetween 5 and 100 Hz. In this arrangement, the second and third outputconnections are preferably connected one to the other via a capacitor,typically one having a value of between 1 and 10 nF. The switchingcircuit is conveniently housed in the electrosurgical instrument,although it can alternatively be housed in the electrosurgicalgenerator.

Conveniently, the controller within the generator is adapted todetermine The timing of the changes between the first and second partsof the combined signal, and the switching circuit is synchronised tooperate in response thereto, so as to deliver the first and second partsof the combined signal respectively to the first and second pairs ofelectrodes. Alternatively, the switching circuit is adapted to determinethe timing of the changes between the first and second parts of thecombined signal, and the controller is adapted to operate in responsethereto.

Where the combined signal is provided by first and second RF sourcesacting simultaneously, means for connecting the waveform convenientlycomprises one or more output stages arranged such that the cutting RFwaveform from the first RF source is delivered between a first pair ofthe three or more electrodes, and the coagulating waveform from thesecond RF source is delivered between a second pair of the three or moreelectrodes. In this way the first and second sources are “hard wired” todeliver their respective waveforms to different output connections, andhence to different pairs of electrodes. Thus the need for activeswitching of the connections using a switching circuit is avoided, butthe power requirements needed for the operation of two RF sources maymake this construction unsuitable for some arrangements, such as thosein which the generator system is housed within the handpiece of theelectrosurgical instrument.

The invention further resides in an electrosurgical system including agenerator system for generating RF power, and an electrosurgicalinstrument including at least three electrodes, the generator systemcomprising at least one RF output stage, means for supplying power tothe at least one output stage, and a controller operable to limit theradio frequency output voltage developed by the at least one outputstage to at least a first predetermined threshold value for cutting orvaporisation and a second threshold value for coagulation and, in acombined mode, to deliver waveforms limited to both first and secondthreshold values, the electrosurgical system also including means forcoupling the waveform to the three or more electrodes such that, in thecombined mode, a waveform limited to the first threshold value forcutting or vaporisation is delivered between a first pair of the threeor more electrodes, and a waveform limited to the second threshold valuefor coagulation is delivered between a second pair of the three or moreelectrodes.

The invention further resides in an electrosurgical generator forsupplying RF power to an electrosurgical instrument, the generatorcomprising at least one RF output stage, three more output connectionsfor the delivery of RF power to the electrosurgical instrument, meansfor supplying power to the at least one output stage, a controlleroperable to limit the RF output voltage developed by the at least oneoutput stage to at least a first predetermined threshold value forcutting or vaporisation and a second threshold value for coagulationand, in a combined mode, to deliver waveforms limited to both first andsecond threshold values, and means for feeding the waveforms to thethree or more output connections such that, in the combined mode, thewaveform that is limited to the first threshold value for cutting orvaporisation is delivered between a first pair of the three or moreoutput connections, and the waveform that is limited to the secondthreshold value for coagulation is delivered between a second pair ofthe three or more output connections.

The invention further resides in an electrosurgical system including agenerator for generating RF power, and an electrosurgical instrumentincluding at least two electrodes, the generator comprising a RF outputstage having two or more output connections, each in electricalconnection with a respective one of the at least two electrodes, a powersupply coupled to the output stage for supplying power to the outputstage, a controller operable to limit the RF output voltage developedacross the output connections to at least a first predeterminedthreshold value for cutting or vaporisation and a second threshold valuefor coagulation and, in a blend mode, to alternate constantly betweenthe first and second threshold values, and adjustment means, operable bya user of the electrosurgical system, for varying the ratio of the blendmode so as to vary the part of the blend signal that is limited to thefirst threshold value for cutting or vaporisation, as compared with thepart of the blend signal that is limited to the second threshold valuefor coagulation.

The electrosurgical system of U.S. Pat. No. 6,416,509 is such that thefrequency of the blended signal can be pre-set to match the type ofelectrode intended for use. There is nothing in U.S. Pat. No. 6,416,509to suggest that the blend ratio (i.e. the ratio of that part of theblended signal that is a cutting or vaporisation signal, as comparedwith that part which is a coagulation signal) can be pre-set, let aloneeasily adjusted by the user of the system. Preferably the adjustmentmeans is carried by the electrosurgical instrument, but the adjustmentmeans can also conceivably be mounted on the generator.

The invention further resides in a electrosurgical system comprising:

-   -   a generator system for generating radio frequency (RF) power,        and an electrosurgical instrument including an instrument shaft,        at the distal end of which is an electrode assembly including at        least three electrodes, the generator system comprising:    -   one or more sources of RF output power, and (ii) a controller        operable to control the generator system such that it is capable        of delivering a first RF waveform to the electrosurgical        instrument or a second RF waveform to the electrosurgical        instrument, and, in a combined mode, to deliver both first and        second RF waveforms, the electrosurgical system further        comprising means for feeding the RF waveforms to the three or        more electrodes such that, in the combined mode, the first RF        waveform is delivered between a first pair of the three or more        electrodes, and the second RF waveform is delivered between a        second pair of the three or more electrodes, and the controller        is operable to cause the feeding means to switch constantly        between delivering the first RF waveform between the first pair        of electrodes and delivering the second RF waveform between the        second pair of electrodes, the first and second RF waveforms        being different one from the other.

As noted above, the present invention includes a controller operable tolimit the RF output voltage developed by the at least one output stageto at least a first predetermined threshold value for cutting orvaporisation and a second threshold value for coagulation, and, in acombined mode, to deliver waveforms limited to both first and secondthreshold values.

Alternatively, in the combined mode, controller can be operable todeliver waveforms limited to either first threshold value or the secondthreshold value. In this embodiment, the means for coupling the waveformto the three or more electrodes, in the combined mode, delivers awaveform limited to either the first threshold value or the secondthreshold value between first and second pairs of the three or moreelectrodes.

Thus, in one embodiment, both the first and second RF waveforms arecutting RF waveforms designed to produce the electrosurgical cutting oftissue. As the first and second waveforms are supplied to different setsof electrodes, the width of the RF cut produced by the electrosurgicalinstrument can be varied by increasing or decreasing the proportion ofthe first and second RF signals supplied to the instrument.

In an alternative embodiment, both the first and second RF waveforms arecoagulating RF waveforms designed to produce the electrosurgicalcoagulation of tissue. In this arrangement, the width of the RFcoagulation lesion produced by the electrosurgical instrument can bevaried by increasing or decreasing the proportion of the first andsecond RF signals supplied to the instrument.

The invention will be further described below, by way of example only,with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an electrosurgical system in accordancewith the present invention,

FIG. 2 is a block diagram of the generator of FIG. 1,

FIG. 3 is a schematic perspective view of an electrosurgical instrumentused as a part of the system of FIG. 1,

FIG. 4 is a schematic diagram of a switching circuit used in the systemof FIG. 1,

FIGS. 5A and 5B are circuit diagrams of two electronic switching devicesfor the switching circuit of FIG. 4,

FIG. 6 is a schematic diagram of an alternative embodiment of switchingcircuit which can be used in the system of FIG. 1,

FIG. 7 is a block diagram of a generator in accordance with FIG. 2,incorporating a switching circuit in accordance with FIG. 4,

FIGS. 8A to 8C are diagrams illustrating techniques for adjusting ablend switching ratio, FIGS. 8A and 8C being circuit diagrams ofalternative ratio adjusting devices and FIG. 8B being a waveform diagramillustrating the operation of the device of FIG. 8A,

FIG. 9 is a block diagram of an alternative embodiment of generatorsystem in accordance with the present invention,

FIG. 10 is a block diagram of a further alternative system in accordancewith the invention, and

FIGS. 11A and 11B are yet further alternative systems for feeding cutand coagulation outputs automatically to different respective electrodepairs.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

Referring to FIG. 1, a generator 10 has an output socket 10S providing aradio frequency (RF) output for an instrument 12 via a connection cord14. Activation of the generator may be performed from the instrument 12via a connection in cord 14 or by means of a footswitch unit 16, asshown, connected to the rear of the generator by a footswitch connectioncord 18. In the illustrated embodiment footswitch unit 16 has twofootswitches 16A and 16B for selecting a coagulation mode and a cuttingmode of the generator respectively. The generator front panel has pushbuttons 20 and 22 for respectively setting coagulation and cutting powerlevels, which are indicated in a display 24. Push buttons 26 areprovided as an alternative means for selection between coagulation andcutting modes.

Referring to FIG. 2, the generator comprises a radio frequency (RF)power oscillator 60 having a pair of output lines 60C for coupling tothe instrument 12. The instrument 12 is shown in FIG. 2 in the form ofan electrical load 64. Power is supplied to the oscillator 60 by aswitched mode power supply 66. In the preferred embodiment, the RFoscillator 60 operates at about 400 kHz, with any frequency from 300 kHzupwards into the HF range being feasible. The switched mode power supplytypically operates at a frequency in the range of from 25 to 50 kHz.Coupled across the output lines 60C is a voltage threshold detector 68having a first output 68A coupled to the switched mode power supply 16and a second output 68B coupled to an “on” time control circuit 70. Amicroprocessor controller 72 coupled to the operator controls anddisplay (shown in FIG. 1) is connected to a control input 66A of thepower supply 66 for adjusting the generator output power by supplyvoltage variation and to a threshold-set input 68C of the voltagethreshold detector 68 for setting peak RF output voltage limits.

In operation, the microprocessor controller 72 causes power to beapplied to the switched mode power supply 66 when electrosurgical poweris demanded by the surgeon operating an activation switch arrangementwhich may be provided on a hand-piece or footswitch (see FIG. 1). Aconstant output voltage threshold is set independently on the supplyvoltage via input 68C according to control settings on the front panelof the generator (see FIG. 1). Typically, for desiccation or coagulationthe threshold is set at a desiccation threshold value between 150 voltsand 200 volts. When a cutting or vaporisation output is required thethreshold is set to a value in the range of from 250 or 300 volts to 600volts. These voltage values are peak values. Their being peak valuesmeans that for desiccation at least it is preferable to have an outputRF waveform of low crest factor to give maximum power before the voltageis clamped at the values given. Typically a crest factor of 1.5 or lessis achieved. When a combined mode output is required, the voltage outputset via input 68C is constantly alternated between the value fordesiccation or coagulation and the value for cutting or vaporisation, toform a blended signal.

When the generator is first activated, the status of the control input601 of the RF oscillator 60 (which is connected to the “on” time controlcircuit 70) is “on”, such that the power switching device which formsthe oscillating element of the oscillator 60 is switched on for amaximum conduction period during each oscillation cycle. The powerdelivered to the load 64 depends partly on the supply voltage applied tothe RF oscillator 60 from the switched mode power supply 66 and partlyon the load impedance 64. The voltage threshold for a desiccation outputis set to cause trigger signals to be sent to the “on” time controlcircuit 70 and to the switched mode power supply 66 when the voltagethreshold is reached. The “on” time control circuit 70 has the effect ofvirtually instantaneously reducing the “on” time of the RFoscillator-switching device. Simultaneously, the switched mode powersupply is disabled so that the voltage supplied to oscillator 60 beginsto fall. The operation of the generator in this way is described indetail in our European Patent Application No. 0754437, the disclosure ofwhich is hereby incorporated by way of reference.

FIG. 3 shows one possible design for the electrosurgical instrument 12.The instrument 12 comprises an instrument shaft 5 at the distal end ofwhich is an electrode assembly shown generally at 8. The electrodeassembly 8 comprises a central cutting electrode 2 disposed between twolarger coagulation electrodes 3 and 40. Insulating layer 4 separates thecutting electrode 2 from the first coagulating electrode 3, while aninsulating layer 41 separates the cutting electrode 2 from the secondcoagulation electrode 40. The cutting electrode 2 protrudes slightlybeyond the two coagulating electrodes.

When the user intends the instrument to cut tissue, the generatorapplies a cutting RF signal between the cutting electrode 2 and one orboth of the two coagulating electrodes 3 and 40. Conversely, when theuser intends the instrument to coagulate tissue, the generator applies acoagulating RF signal between the two coagulating electrodes 3 and 40.The application of the blended RF signal will be described withreference to the switching circuit shown in FIG. 4.

FIG. 4 shows a switching circuit shown generally at 45 and comprisinginput connections 46 and 47 connected respectively to the two outputlines 60C of the generator 10. Switching circuit 45 has three outputconnections 48, 49 and 50. Output connection 48 is connected to thecutting electrode 2 in the device of FIG. 3. Output connections 49 and50 are respectively connected to the coagulating electrodes 3 and 40 inthe device of FIG. 3. An electronic switch device 51 is connectedbetween output connections 48 and 49. The switch 51 is capable ofrapidly making and breaking the connection between the output lines 48and 49. A capacitor 53 is connected between the output connections 49and 50, the capacitor typically having a value of between 1 and 10 nF.

When the user actuates the footswitches 16A or 16B to operate theinstrument 12 in the blended mode, the generator supplies alternatingbursts of the RF cutting and coagulating signals to the inputconnections 46 and 47. The switch device 51 operates synchronised withthe alternating RF signals such that when that part of the signalcontaining the cutting signal is received, the switch device is opensuch that there is open circuit between the output connections 48 and49. Thus the cutting RF signal is supplied between cutting electrode 2and coagulating electrode 40, via output connections 48 and 50respectively. Conversely, when that part of the signal containing thecoagulating voltage is received across the input connections 46 and 47,the switching device 51 is closed such that output connections 48 and 49are in electrical communication one with the other. Thus, during thecoagulation part of the blended signal, the signal is supplied betweenthe two coagulation electrodes 3 and 40, via output connections 49 and50, with the capacitor 53 providing a potential difference therebetween.

Switching device 51 may comprise an AC opto-relay such as the opticallycoupled dual FET arrangement shown in FIG. 5A. Another switching deviceproviding isolation between control circuitry and the output lines isthe combination of an AC bridge and a single MOSFET switch controlledvia an isolating driver, a shown in FIG. 5B.

The above description is based upon the generator 10 controlling theblended mode signal, and the switching device 51 opening and closingsynchronously therewith. However, this does not have to be the case andthe switching device can control the generator in order to determine thechangeover between the cutting and coagulation RF signals.

Consider the switching circuit 45 as shown in FIG. 4. When the switchingdevice 51 is in its open condition, the cutting signal is suppliedacross output connections 48 and 50. When the switching device 51closes, the cutting signal is initially supplied between the outputconnections 49 and 50, separated by the capacitor 53. This causes thecurrent delivered by the generator to rise rapidly such that the currentlimiting circuitry within the generator operates to reduce the powerbeing delivered, such that the signal rapidly converts to an RF signaltypical for coagulation. The effect of the current limiting circuitrywithin the generator is that the closing of the switching device 51causes the signal being delivered to be transformed, almostinstantaneously, from a cutting signal to a coagulating signal.Conversely, when the switching device 51 opens again, the generatorceases to be current limited, and the signal once again rapidly revertsto being a cutting RF signal. In this way, the opening and closing ofthe switching device 51 toggles the generator between its cutting andcoagulating modes, producing the blended signal which is supplied to theelectrodes of the instrument 12.

FIG. 6 shows an alternative embodiment of switching circuit, which canbe employed if the generator 10 is not a current limited generator, orif it is desired not to use the current limiting features of thegenerator. The switching circuit of FIG. 6 is almost identical to thatof FIG. 4, the main difference being the addition of an additionalcapacitor 52 in series with the input connection 46. The capacitor 52typically has a value one half of that of capacitor 53, such that thevoltage delivered across output connections 49 and 50 is divided down toa level typically used for coagulation without reducing the power outputof the generator 10. In this way a cutting RF signal is deliveredbetween output connections 48 and 50 when the switching device 51 isopen, and a coagulating RF signal is delivered between outputconnections 49 and 50 when the switching device is closed.

Switching circuit 45 can be provided within the electrosurgicalinstrument 12, or within the output stage of the generator 10 as shownin FIG. 7. Wherever the switching circuit 45 is located, the switchingdevice can be provided with an adjustment device 55, (as shown in FIG.6) operable by the user of the system in order to adjust the timing ofthe switching device. By operating the adjustment device 55, the user isable to alter the ratio between that part of the blended RF signal whichis a cutting signal, and that part which is a coagulating signal.Whether the adjustment device 55 is located on the instrument 12 or thegenerator 10, the user of the system can vary the signal so as toincrease or decrease the coagulating component of the blended signalwith respect to the cutting component, and vice versa. This givesconsiderable flexibility to the electrosurgical system in terms of itsuse as a simultaneous cutting and coagulation device, with user-operablecontrol of how much coagulation is provided.

As in the arrangement described above in FIG. 4, the switching device 51of the alternative switching circuit of FIG. 6 may be as shown in Figure5A or Figure 5B, the driving signal being obtained from a sourceassociated with the switching device itself or from control circuitrywithin the generator which controls other generator functions.

Various circuits for implementing the adjustment device 55 will beapparent to those skilled in the art. An example of a circuit in which ablended mode signal is generated by elements associated with theswitching device and has a variable mark-to-space ratio is shown in FIG.8A. In this case, the output of a triangular wave generator 56 iscompared in a comparator 57 with a user-adjustable reference voltage toproduce a square wave of the switching device 51 (FIG. 6). Anothercircuit generating an adjustable blended mode switching device controlsignal is shown in FIG. 8C. Here, a user-operable potentiometer 58 iscoupled with a timer circuit 59 using a 555 i.c.

FIG. 9 shows an alternative generator system in which two RF sourcecircuits 74 and 74′ are employed. Source circuit 74 comprises RFoscillator 60 and its associated power supply and control elements. Thesource circuit is as described with reference to FIG. 2, and likeelements are given the same reference numerals as in FIG. 2. The secondsource circuit 74′ comprises a second RF oscillator 60′, along with asecond controller 72′, power supply 66′, voltage threshold detector 68′and on time control circuit 70′. FIG. 9 shows the source circuit 74′ ashaving its own dedicated version of each of these units, although it isfeasible that certain of them (such as the power supply 66′ andcontroller 72′) could be shared with the source circuit 74. The voltagethreshold detector 68 is set such that the output connections 60C fromsource circuit 74 provide an output power signal having a cutting RFwaveform, while the voltage threshold detector 68′ is set such that theoutput connections 60C′ from source circuit 74′ provide an output powersignal having a coagulating RF waveform. The second oscillator 60′operates at a different frequency from that of oscillator 60.

A common output stage 73 is provided for both source circuits 74 and74′. Output connections 60C from source circuit 74 are connected toinput connections 46 and 47 of the output stage 73, while outputconnections 60C′ from source circuit 74′ are connected to inputconnections 46′ and 47′ of the output stage respectively. Within theoutput stage 73, input connections 47 and 47′ are both connected tooutput connection 49, while input connection 46 is connected to outputconnection 48, and input connection 46′ to output connection 50. Theresult of this arrangement is that the cutting RF signal from sourcecircuit 74 is delivered between output connections 48 and 49 and henceto one pair of electrodes on the electrosurgical instrument 12.Simultaneously, the coagulating RF signal from source circuit 74′ isdelivered between output connections 49 and 50 and hence to a differentpair of electrodes of the instrument 12. Thus the electrosurgicalinstrument 12 is able simultaneously to cut and coagulate tissue byvirtue of the two different frequency signals. As before, the advantageis that the cutting signal and the coagulating signal, whether they beapplied simultaneously or in an alternating blended signal, aredelivered to different pairs of electrodes of the electrosurgicalinstrument. The design of these electrodes can therefore be optimised,depending on whether they are intended to cut or coagulate tissue.

Referring to FIG. 10, in an further alternative generator and instrumentcombination, two RF power oscillators 60-1 and 60-2 are powered from acommon power supply 62 and are controlled by a common controller 72 toproduce on respective output lines 60C an RF power signal suitable forcutting and an RF power signal suitable for coagulation. These signalsmay be fed to a switching circuit 63 for selecting the power signal fromone oscillator 60-1 or the other oscillator 60-2 according to inputsfrom, for instance, foot switches, the selected power signal beingtransmitted on output connections 80, 81. In a blended mode, the switchis operated repeatedly at a predetermined rate to produce a blendedoutput power signal across connections 80, 81. The power oscillators60-1, 60-2 are operated at different frequencies, and the respective cutand coagulation signals are fed to the required electrodes by feedingthe power signal on output connections 80, 81 to tuned circuits 82-1 and82-2 tuned to the different frequencies. The outputs of the tunedcircuits are_coupled via electrode lines 48, 49 and 50 to the respectiveelectrodes of the electrosurgical instrument. In this way, the cuttingsignal from oscillator 60-1 is fed to a cutting electrode 48 and acommon electrode 49, whereas the coagulation signal from oscillator 60-2is fed to a coagulation electrode 50 and the common electrode 49.

In the embodiment shown in FIG. 10, the connection between theelectrosurgical generator and the electrosurgical instrument istypically provided by output connections 80 and 81, but theapportionment of circuit blocks between the generator and the instrumentmay be varied.

Further embodiments are shown in FIGS. 11A and 11B. Like the embodimentof FIG. 9, these embodiments dispense with the need for a signal routingswitch or switching circuit.

Referring to FIG. 11, there are provided two tuned circuits 82-1 and82-2 (as in FIG. 10), tuned to different frequencies. Each has aseries-resonant inductor-capacitor pair 84 and a parallel-resonantinductor-capacitor pair 86, the latter being transformer coupled tooutput connections 46 and 47 on the one hand and 46′ and 47′ on theother hand. As in the embodiment of FIG. 10, each tuned circuit has twoinputs, one of which is connected to a generator output connection 80and the other of which is connected to a generator output connection 81.In this embodiment, the generator has an output stage comprising RFswitches arranged in two oppositely acting push-pull pairs 90A, 90B and91A, 91B. Typically these switches comprise power MOSFETS. Each switch90A, 90B, 91A, 91B is connected to driver inputs 92, 93, as shown, whichreceive an RF drive signal which, for producing on the outputconnections 80, 81 an output having a cut waveform is at one RFfrequency, and for producing a coagulation output on the outputconnections 80, 81, has a different RF frequency, these frequenciesbeing, respectively, the resonant frequency of, the resonantcombinations 84, 86 of the first tuned circuit 82-1 and, the resonantfrequency_of the corresponding resonant combinations of the other tunedcircuit 82-2. As described above, the RF switches 90A, 90B, 91A and 91Bof the generator output stage may be driven according to, for instance,a footswitch control to produce a cut output or a coagulation output.Again, additionally, a blended output may be produced in which the RFfrequency alternates constantly between the two resonant frequencies ofthe tuned output circuits.

The embodiment of FIG. 11B is a modification of that of FIG. 11A,in_which the generator output stage has a single push-pull pair of RFswitches 90A, 90B and in which the tuned circuits each have one inputconnected to the junction between the switches 90A, 90B and the otherinput connected to ground.

Referring back to FIG. 3, the blended signal supplied alternately to theelectrodes 2 and 3, or 3 and 40, is not necessarily a blend of cuttingand coagulating signals. Both constituent parts of the blended signalcould conceivably be cutting RF signals. A cutting signal suppliedbetween electrodes 3 and 40 would produce a much wider RF cut than acutting signal supplied between electrodes 2 and 3, or 2 and 40. Thus,by varying the amount of the first RF signal (supplied betweenelectrodes 2 and 3) as compared to the second RF signal (suppliedbetween electrodes 3 and 40), the width of the RF cut can be varied.

Similarly, both constituent parts of the blended signal couldconceivably be coagulating RF signals. A coagulating signal suppliedbetween electrodes 3 and 40 would produce a much wider RF lesion than acoagulating signal supplied between electrodes 2 and 3, or 2 and 40.Thus, by varying the amount of the first RF signal (supplied betweenelectrodes 2 and 3) as compared to the second RF signal (suppliedbetween electrodes 3 and 40), the width of the RF lesion can be varied.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiment, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

1. An electrosurgical system comprising: a generator system forgenerating radio frequency (RF) power, and an electrosurgical instrumentincluding an instrument shaft, at the distal end of which is anelectrode assembly including at least three electrodes, the generatorsystem comprising: (i) one or more sources of RF output power, and (ii)a controller operable to control the generator system such that it iscapable of delivering a first RF waveform to the electrosurgicalinstrument or a second RF waveform to the electrosurgical instrument,and, in a combined mode, to deliver both first and second RF waveforms,the electrosurgical system further comprising means for feeding the RFwaveforms to the three or more electrodes such that, in the combinedmode, the first RF waveform is delivered between a first pair of thethree or more electrodes, and the second RF waveform is deliveredbetween a second pair of the three or more electrodes, and thecontroller is operable to cause the feeding means to switch constantlybetween delivering the first RF waveform between the first pair ofelectrodes and delivering the second RF waveform between the second pairof electrodes, the first and second RF waveforms being different onefrom the other.
 2. An electrosurgical system according to claim 1,wherein the generator system comprises a single source of RF power, and,in the combined mode, the controller is operable to cause the generatorsystem to alternate constantly between delivering the first RF waveformand the second RF waveform.
 3. An electrosurgical system according toclaim 2, wherein the means for connecting the waveform comprises aselection arrangement for varying the coupling between the source andthe three or more electrodes such that, in the combined mode, a firstpart of the combined signal that is the first RF waveform is deliveredbetween a first pair of the three or more electrodes, and a second partof the combined signal that is the second RF waveform is deliveredbetween a second pair of the three or more electrodes.
 4. Anelectrosurgical system according to claim 3, wherein the selectionarrangement is a switching circuit comprising first and second inputconnections, first second and third output connections, and anelectronic switch connected between the first and second outputconnections, and being adapted to open and close in order to connect thefirst and second output connections periodically one to the other.
 5. Anelectrosurgical system according to claim 4, wherein the electronicswitch opens and closes at a frequency of between 5 and 100 Hz.
 6. Anelectrosurgical system according to claim 4, wherein the second andthird output connections are connected one to the other via a capacitor.7. An electrosurgical system according to claim 6, wherein the capacitorhas a value of between 1 and 10 nF.
 8. An electrosurgical systemaccording to claim 3, wherein the selection arrangement is housed withinthe electrosurgical instrument.
 9. An electrosurgical system accordingto claim 3, wherein the selection arrangement is housed within theelectrosurgical generator.
 10. An electrosurgical system according toclaim 3, wherein the controller is adapted to determine the timing ofthe changes between the first and second parts of the combined signal,and the selection arrangement is synchronised to operate in responsethereto.
 11. An electrosurgical system according to claim 3, wherein theselection arrangement is adapted to determine the timing of the changesbetween the first and second parts of the combined signal, and thecontroller is adapted to operate in response thereto.
 12. Anelectrosurgical system according to claim 1 wherein both the first andsecond RF waveforms are cutting RF waveforms designed to produce theelectrosurgical cutting of tissue.
 13. An electrosurgical systemaccording to claim 1 wherein both the first and second RF waveforms arecoagulating RF waveforms designed to produce the electrosurgicalcoagulation of tissue.
 14. An electrosurgical system including agenerator system for generating radio frequency (RF) power, and anelectrosurgical instrument including at least three electrodes, thegenerator system comprising (i) at least one RF output stage, (ii) meansfor supplying power to the at least one output stage, and (iii) acontroller operable to limit the RF output voltage developed by the atleast one output stage to at least a first predetermined threshold valuefor cutting or vaporisation and a second threshold value for coagulationand, in a combined mode, to deliver waveforms limited to either thefirst threshold value or the second threshold value, the electrosurgicalsystem also including means for coupling the waveform to the three ormore electrodes such that, in the combined mode, a waveform limited toeither the first threshold value or the second threshold value isdelivered between first and second pairs of the three or moreelectrodes.
 15. An electrosurgical system according to claim 14, whereinthe adjustment means is carried by the electrosurgical instrument. 16.An electrosurgical system according to claim 14, wherein the adjustmentmeans is mounted on the generator.